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Linear or Nonlinear Modeling for ENSO Dynamics?

ISMAR-CNR, 19032 La Spezia, Italy
NOAA-ESRL, Physical Sciences Division, University of Colorado, CIRES, Boulder, CO 80305, USA
Physics Department, Pisa University, 56127 Pisa, Italy
Author to whom correspondence should be addressed.
Atmosphere 2018, 9(11), 435;
Received: 12 September 2018 / Revised: 31 October 2018 / Accepted: 4 November 2018 / Published: 8 November 2018
(This article belongs to the Special Issue El Niño Southern Oscillation (ENSO))
PDF [4888 KB, uploaded 8 November 2018]


The observed ENSO statistics exhibits a non-Gaussian behavior, which is indicative of the presence of nonlinear processes. In this paper, we use the Recharge Oscillator Model (ROM), a largely used Low-Order Model (LOM) of ENSO, as well as methodologies borrowed from the field of statistical mechanics to identify which aspects of the system may give rise to nonlinearities that are consistent with the observed ENSO statistics. In particular, we are interested in understanding whether the nonlinearities reside in the system dynamics or in the fast atmospheric forcing. Our results indicate that one important dynamical nonlinearity often introduced in the ROM cannot justify a non-Gaussian system behavior, while the nonlinearity in the atmospheric forcing can instead produce a statistics similar to the observed. The implications of the non-Gaussian character of ENSO statistics for the frequency of extreme El Niño events is then examined. View Full-Text
Keywords: non-Hamiltonian complex systems; Fokker–Planck equation; transport coefficients; El Niño-La Niña; Lie evolution; projection approach non-Hamiltonian complex systems; Fokker–Planck equation; transport coefficients; El Niño-La Niña; Lie evolution; projection approach

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Bianucci, M.; Capotondi, A.; Mannella, R.; Merlino, S. Linear or Nonlinear Modeling for ENSO Dynamics? Atmosphere 2018, 9, 435.

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